which exhaust? - JeepForum.com

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post #1 of 3 Old 09-27-2001, 10:27 AM Thread Starter
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which exhaust?

I'm changing the the 4.2 head to the 4.0 head in a '89 yj. Which exhaust will work with this application? is the Borla header worth the extra bucks? and which model would I order ?. I will need the o2 sensor port.

89 yj w/ mopar mpi and 4.0 head.94 ax-15 tranny and t-case, more mods comin.
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post #2 of 3 Old 09-27-2001, 12:25 PM
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1994 YJ Wrangler 
Join Date: Jul 2001
Location: Oceanside, CA, USA
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I've not been exceptionally impressed with the build quality of Borla headers I've seen in the past. The header tubes seem a bit thin, and I'm leery of their welds. However, it's been a while, so maybe they've improved since I last experienced one...?

Personally, I have a Thorley header and I love it. The part number is 634Y for F.I. heads. If your 4.0 head is off a fuelie Jeep, it should bolt right on.

Both the Thorley and the Borla have CARB EO numbers, and thus both have the O2 bung.

'94 YJ Sahara Hardtop
4.0L / AX-15 / Stock NP231 / Stock D30 (open) / D60 (35-spline, Detroit locker, Moser axles) / rear disc brakes / 4.56 gears / Advanced Adapters SYE & CV Shaft / 33" BFG MT-KM's / Thorley Header / Magnaflow Muffler / BesTop Flares
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post #3 of 3 Old 09-27-2001, 04:10 PM
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borlas work fine, but i believe custom made exhaust systems (by a specialist-important) can optimize the performance in the best way
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